“I just didn’t like this constant pressure to improve myself,” Bertram said, adding that he is the antithesis of many young people in Berlin: Skinny, well-groomed but stressed.

Club activities include swaying back and forth, like in a beer hall; the “Tarzan yell” beating your chest with your fists and yelling; and the potato chip competition, consisting of eating a plastic cup full of chips without using one’s hands a favourite among the club’s child members.

The club has been meeting for about a year at bars and pubs in the German capital and now boasts 25 members from 8 to 64 years old. Men, women and children are all welcome. Bertram’s wife initially thought sofa sports was “nonsense” but she joined anyway, Bertram said with a smug smile.

The father of two, who works in political communications, sports a goatee and has a penchant for cycling shirts that are too tight around the belly. He speaks with eyes full of mischief, suggesting one shouldn’t take everything he says at face value.

Lounging on a worn-out couch at one of his favourite bars in Berlin, Bertram said the club only meets in bars with sofas, where everyone is encouraged to participate in the club’s unique fitness program.

The association’s “sofa exercises” aren’t just bar games, Bertram said with a deadpan expression. Some strengthen back and arm muscles, or burn calories. The beer-hall sway, for example, is said to combine popular German traditions with eastern-Asian forms of body awareness including elements from the Chinese Qigong system of body co-ordination.

“We are no regular couch potatoes because we’re not idling away our time in front of the TV,” he said. “We’ve put some serious thought into this.”

It was the traditional beer-mug hoisting that convinced Patricia Bernreuther to join the club.

“It’s really just a variety of what we’ve been doing in Bavaria for generations,” the 28-year-old parliamentary aide said while holding a heavy glass of beer in her outstretched hand with ease. “It makes me feel like I’m back home.”

Unlike southern Germans, who competitively carry more than 20 mugs at the same time, the Berliners are satisfied to exercise with one glass at a time, at a sloth-like speed. Most importantly, sessions are fun.

Norbert Buddendick, a 50-year-old lobbyist, said the couch potato meetings are much more fulfilling than his previous gym workouts.

“I like the whole-body approach,” he said, tongue-in-cheek, as he ordered another glass of wheat beer. “And it’s really great to mingle with like-minded people.”

It’s not just fun and games ‚Äî the club wouldn’t be German without some serious rules and order. Bertram has taken out accident insurance for the group, registered it with fiscal authorities and applied for membership in the regional sports association.

And the couch potatoes have their own ambitions, too.

“We are convinced that we will grow and expand across country borders,” Bertram said. “For 2019, we envision a European championship in sofa sport exercises.”